Have you checked with any of the dept stores currently having sales?
Bloomingdales is running their Friends & Family event right now -- in fact, Sunday is the last day. MJ bags are 20% off (some of the styles have already been marked down 30%, so they're an addtl 20% off of that - but I don't believe the Mercer Blake is one of those)
Then on Tuesday, NM is having their semi-annual "Private Night" sale -- where certain designer bags will be 30% for one day only -- they haven't released the list of eligible designers yet (that gets released on Monday), but the SA I talked to today thought that MJ would be included. They are also starting their First Call Sale (end of season clearance), where certain styles will be permanently marked down 30% (until Last Call a few weeks later, when they are marked down again). I'd be surprised, tho, if the Mercer Blake was included in 1st call.
Finally, Barney's in Dallas, TX is having a one-day only event on Monday (5/5) -- MJ bags are 40% off. They've been pre-selling since Wednesday, so I don't know what is left by now, but it's certainly worth a phone call to see if they have it!!
Here are some phone #s for you:
Bloomingdales, Chicago (Michigan Avenue) - 312/440-4563
Barneys, Dallas, TX - 469/221-4700
You can call any NM (#s on the website) to get info re: Private Night
Good Luck -- I hope you find your bag!